1. Field of the Invention
The present invention relates to a semiconductor laser apparatus comprising cavities in correspondent with a plurality of light emitting units fabricated on the same substrate, and a laser coupler, a data reproduction apparatus and a data recording apparatus having the semiconductor laser apparatus, and a production method of the semiconductor laser apparatus.
2. Description of the Related Art
In recent years, an apparatus capable of recording and reproducing of a plurality of media such as CD (compact disk) and DVD (digital versatile disk) has been developed. When single apparatus is used to record/reproduce a plural types of media, the apparatus is required to have a system construction satisfying all the standards of media types included in the system. For example, at least two laser light emitting devices with different wavelengths have to be equipped in the same apparatus so as to perform recording/reproducing of both the CD and the DVD, that use laser lights with different wavelengths.
The device emitting laser lights with two different wavelengths may be realized by combining separate semiconductor laser devices emitting the two wavelengths and respective optical systems for the separate semiconductor laser devices. However, the combination of the separate devices and the optical systems may causes increase of a number of parts and a total cost of the apparatus, and prevent reduction of the apparatus size.
To resolve such disadvantages, a monolithic type semiconductor laser device had been developed. The monolithic type semiconductor laser device (so called two wavelength laser) has two active layers grown on the same substrate separately for emitting different wavelength lasers. FIGS. 10A and 10B are explanatory schematics illustrating a monolithic type semiconductor laser device. FIG. 10A is a plan view of the monolithic type semiconductor laser device. FIG. 10B is a cross sectional view showing a cross section taken on line X-Xxe2x80x2 in FIG. 10A.
The semiconductor laser device may be produced, for example, by fabricating a n-GaAs buffer layer 2a on a substrate 1 consisting of n-GaAs, and, a laser diode A emitting 780 nm band wavelength laser light and a laser diode B emitting 650 nm band wavelength laser light on the n-GaAs buffer layer 2a. A separation between light emitting parts of the laser diode A and the laser diode B is less than 200 xcexcm. For example, the separation may be set to less than 100 xcexcm in many cases.
In the monolithic type semiconductor laser with the configuration described above, it is possible to keep a separation between the two laser lights into a smaller value with high precession since the active layers and the clad layers capable of emitting different wavelength laser lights are fabricated separately on the same substrate. Accordingly, an optical system at a subsequent stage may be shared, and it becomes possible to reduce a number of parts, a total cost of the apparatus, and a size of the apparatus.
However, there are some drawbacks in the semiconductor laser devices or apparatus described above despite of its advantages such as having a capability of sharing the same optical system in the subsequent stage and setting a smaller separation between the two laser lights with high precession, that are due to the fact that the laser diodes emitting different wavelength laser lights are fabricated separately on the same substrate. Namely, some of requirements from a system, which may be data reproducing/recoding apparatus using the multiple laser lights, may not be satisfied since cavity lengths in the semiconductor laser are fabricated the same.
For example, in the data reproducing/recording apparatus, there are requirements to optimize data reproduction/recording at 780 nm band laser light for the CD and at 650 nm band laser light for the DVD. However, all the cavity lengths are fabricated the same by cleavage since the both laser diodes are fabricated on the same substrate in the monolithic type semiconductor laser device described above. Accordingly, it is difficult to satisfy all the requirements for reproducing/recording of media using multiple wavelength laser lights.
Furthermore, a cavity of a laser diode may be fabricated to a longer length than necessary since a cavity length of one laser diode is determined by a cavity length of the other laser diode. Accordingly, a current consumption of the one laser diode is increased unnecessarily.
The invention was carried out to resolves such drawbacks. That is, in accordance with an embodiment of the present invention, there is provided a semiconductor laser apparatus comprising a plurality of cavities corresponding to a plurality of light emitting units on a substrate respectively, wherein the plurality of cavities have different cavity lengths.
According to the embodiment of the present invention, the semiconductor laser apparatus, comprising the cavities corresponding to the light emitting units on the same substrate and having different cavity lengths, may be optimized with requirements of a system such as data reproducing/recording apparatus employing the semiconductor laser apparatus therein since the cavity cavity lengths may be individually adjusted to different from one another.
Alternatively, the plurality of cavities in accordance with the present invention may be fabricated to have cavity lengths all less than a length of said substrate. Furthermore, one of the cavities in accordance with the present invention may comprise a three-element type compound semiconductor, and another of the cavities may comprise a four-element type compound semiconductor.